Screw caps are a common form of closure employed to seal a large range of containers such as plastic and glass bottles for liquids including beverages ranging from soft drinks to wine. For bottled wines, screw caps are generally made of aluminium and have now become increasingly popular as a replacement for the traditional cylindrical cork due to concerns about cork taint and variability of quality of cork material which can lead to a poor seal and the associated premature oxidation of wine. While initially screw caps were associated with budget wines they are now commonly used for the packaging of premiums wine due to their inherent reliability.
Referring now to FIG. 1, there is shown a cutaway view of a roll on tamper evident (ROTE) screw cap 100 for a wine bottle 200. Screw cap 100 consists of an outer sleeve 110 formed of a malleable aluminium alloy which is rolled on to the opening 250 of bottle 200. Screw cap 100 further incorporates a wad or liner 120 which seats within the roof of the screw cap 100 and which forms a seal against the rim 220 of the bottle or container 200. Wad 120 may be formed of any number of materials ranging from plastic such as polyvinylidene chloride (PVDC), cork, rubber or multilayer combinations of these materials. In this example, the sealing layer 130 of wad 120 is formed from PVDC.
Screw caps of the type illustrated in FIG. 1 and more generally have the significant disadvantage that they are not suitable to seal a container containing a liquid that is at a high internal pressure. As an example, many sparkling varieties of wine are sealed at high pressure and the screw cap is simply not able to withstand the internal pressure exerted by the contents of the bottle. Accordingly, it is then necessary to use traditional cylindrical corks with all of their associated disadvantages. In an earlier filed patent application (PCT Application No. PCT/AU2010/00237) the present applicant disclosed a sealing member for a closure suitable for the sealing of bottles containing liquids at high pressure such as sparkling wines and the like. While the disclosed arrangement has provided acceptable performance, the applicant has developed further improvements which are now the subject of this application.